program lagrange
implicit none
real(8),dimension(:,:),allocatable::a
real(8),dimension(:),allocatable::l
integer::i,j,k,n
real(8)::x_r,y
print,"输入已知点的个数n"
read(,)n
allocate(a(n,2),l(n))
print,"顺序输入n个点的坐标值：(x,y)"
read(,)((a(i,j),j=1,2),i=1,n)
print,"输入你想知道的y值所对应的x值:"
read(,)x_r
call lagrange_cz(n,a,x_r,y)
print,"当x=",x_r,"y的数值为：",y
pause
end program lagrange
!****************************************************
subroutine lagrange_cz(n,a,x_r,y)
implicit none
integer::i,j,k,n
real(8),dimension(n,2)::a
real(8),dimension(n)::l
real(8)::x_r,y
y=0
do k=1,n
l(k)=1
do i=1,n
if(i/=k)then
l(k)=l(k)(x_r-a(i,1))/(a(k,1)-a(i,1))
endif
end do
y=y+l(k)a(k,2)
enddo
end subroutine lagrange_cz
============================================
program Gauss_Seidel
implicit none
real(8),dimension(:,:),allocatable::a
real(8),dimension(:),allocatable::b,x,x_k1,x_result
integer::i,j,n
print,"输入维度n"
read(,)n
allocate(a(n,n),b(n),x(n),x_k1(n),x_result(n))
print,"输入nn的数组a"
read(,)((a(i,j),j=1,n),i=1,n)
print,"n的数组b"
read(,),b
print,"初始数组x0"
read(,),x
call Gauss_Seidel_dd(n,a,b,x,x_result)
print,"x的数值为：",x_result
pause
end program Gauss_Seidel
!****************************************************
subroutine Gauss_Seidel_dd(n,a,b,x,x_result) ! 书上迭代法
implicit none
integer::i,j,n,k
real(8),dimension(n,n)::a
real(8),dimension(n)::b,x,x_k1,x_result
real(8)::sum1,sum2
do k=1,100 !迭代次数
do i=1,n
sum1=0
do j=1,i-1
sum1=sum1+a(i,j)x_k1(j)
end do
sum2=0
do j=i+1,n
sum2=sum2+a(i,j)x(j)
end do
x_k1(i)=(b(i)-sum1-sum2)/a(i,i)
enddo
x=x_k1 !完成一次迭代
enddo
x_result=x
end subroutine Gauss_Seidel_dd